Creating Holes in Cylinder for Lightsaber
I have a few pictures that I can set up to show you. First, you add 3 loopcuts through the area you are working in. After that, you select 4 faces to make the inset for the rectangle and then 6 for the circle. I select the inner faces after the inset on the area to be turned into a circle, and duplicate it and separate it from the mesh. In object mode, I select that set of faces and use Looptools > Circle to round them into a circle after shifting the view to top view down with selection by pressing Shift Numpad 7. Here I then turn on the magnet and select Faces and then just press G to grab and confirm without moving it - the circle is then projected to the cylinder underneath. Join them back together with ctrl-J and enter edit mode -  and then delete the faces underneath , and scale the circle to fit the hole.  I used alt-M top merge at last by selecting the outer ring vert and then the one in the circle. After completely welded back together, I inset the faces to create another edge loop and then delete the inner faces for the circle and the rectangle.